Exemplary embodiments of the present invention relate to a method and to a main camshaft body for producing a built-up camshaft, and to a built-up camshaft as such, wherein the camshaft that is to be built up or is built up has at least one cam element disposed in a rotationally fixed and axially displaceable manner on a main camshaft body, and at least one cam element disposed in a rotationally fixed and axially non-displaceable manner on the main camshaft body.
In order to be able to operate internal combustion engines in an optimum operating range, the valve train is influenced at regular intervals. For example, it is typical to change the opening times and/or the corresponding valve strokes by means of switchable cams or cam elements formed with various contours. European Patent Document EP 1 503 048 A1 discloses this type of switchable cam or this type of switchable cam element (also designated as a sliding cam). The axially displaceable cam element comprises a tubular sleeve mounted in a rotationally fixed and axially displaceable manner on a camshaft. The axial displacement of the cam element brings a corresponding cam follower into engagement with the various cam curves. In the case of this type of camshaft, not all of the cams or cam elements (or functional elements) routinely have to be disposed in an axially displaceable manner thereon. If a multi-tooth profile is introduced on the common camshaft, the fixed and movable functional elements are secured against rotation on the camshaft by means of the multi-tooth profile.
German Patent Document DE 41 21 951 C1 discloses a camshaft for controlling valves in internal combustion engines, wherein a cam element having a hub, which is enlarged outwardly in the manner of a funnel, is applied in a non-positive manner to a region of a main camshaft body which is roller-burnished and thus enlarged in terms of its outer diameter. One development of this connection is described in PCT International Patent Application Publication No. WO 2004/079163 A1.
In this case, the hub of the cam element has severally inwardly directed extensions, by means of which the cam, which is applied to the roller-burnished region of the main camshaft body, ensures a positive connection in the rotational direction in addition to the non-positive connection in the region of the roller-burnished portion. With regard to this type of non-positive or non-positive/positive attachment, the development of the attachment of axially non-displaceable cam elements on a main camshaft body—as described in German Patent Document DE 41 21 951 C1 and PCT International Patent Application Publication No. WO 2004/079163 A1—is incorporated in its entirety into the disclosure content of the present application.
Furthermore, German Patent Document DE 10 2004 002 301 A1 describes a method of producing a built-up camshaft that likewise produces a built-up camshaft with axially displaceable cam parts. In this case, the displaceable cam elements are constructed in a similar manner and are disposed on the main camshaft body, as has already been described above with reference to European Patent Document EP 1 503 048 A1.
Exemplary embodiments of the present invention are directed to a built-up camshaft and a method and a main camshaft body for producing a built-up camshaft, wherein the camshaft which is built up or is to be built up has cam elements disposed in an axially displaceable and rotationally fixed manner on a main camshaft body (also designated as “switchable cam elements”), and also cam elements disposed in an axially non-displaceable and rotationally fixed manner on a main camshaft body (also designated hereinafter as “fixed cam elements”). During production of a built-up camshaft, superfluous introduction of heat into the components and unnecessary material attenuation are to be omitted where possible. It should also be ensured that in particular the fixed cam elements can be produced in the simplest manner possible and can be aligned in the most precise manner possible in terms of their angular orientation.
In accordance with the inventive method of producing a built-up camshaft both with fixed cam elements and switchable cam elements, a bar-shaped main camshaft body (which is formed in particular as a hollow shaft body) is provided. In an advantageous manner, the main camshaft body has at one end thereof a camshaft end piece formed either as a one-piece component of the main camshaft body or which is connected as a separate component to the main camshaft body in a separate subsequent method step.
In accordance with the invention, the surface of the main camshaft body is machined in such a manner that in at least one first axial sub-section of its surface—e.g., by the introduction, in sections, of a multi-tooth profile (in particular by milling of individual toothed grooves into the main camshaft body surface)—it permits a rotationally fixed and axially displaceable arrangement of cam elements.
Furthermore, the surface of the main camshaft body is machined in such a manner that in at least a second axial sub-section it has a surface region, in which its diameter is enlarged with respect to the first axial sub-section (at least with respect to the minimum diameter of the multi-tooth profile of the first sub-section) as well as with respect to main body sub-sections that are free (i.e., do not have a surface profile formed for an arrangement of cam elements), so that in the enlarged region cam elements can be disposed in a rotationally fixed and non-displaceable manner on the main camshaft body (which optionally have been slid beforehand onto the main camshaft body from a defined thread-on or slide-on direction, with their profile teeth engaging into the profile toothing of the main camshaft body, over one or several multi-tooth region(s) of a first axial sub-section of the main camshaft body). With regard to the non-positive/positive connection to be created between the cam element and the main camshaft body, the content of German Patent Application DE 7 17 190 A1 and PCT International Patent Application Publication No. WO 2004/079163 A1 are also incorporated at this juncture into the disclosure content of this application. In accordance with the types of connection for a non-positive/positive connection of a cam element and main camshaft body, as described in the quoted Prior Art, a main camshaft body is enlarged at a predetermined axial attachment position, so that a cam element which in its axial recess (hub) has radially inwardly directed protrusions (manufactured advantageously by mechanical stripping of the recess) digs with its protrusions in a metal-cutting manner in the region of the enlargement when the cam element is slid onto the main camshaft body, and a non-positive/positive connection is established with the main camshaft body. In a further development of this non-positive/positive connection, a hardenable material (in the form of a filler or the like) is introduced into the intermediate spaces of the structured surface of the main camshaft body which are produced by means of mechanical roller-burnishing, in order to increase the strength of the connection between the cam element and the main camshaft body,
In so doing, the maximum shaft body diameter inside the at least one second axial sub-section is larger in dimension than the minimum inner diameter of a cam element which is to be slid on and is to be positioned in the second sub-section (and of which regions are reduced in size by the radially inwardly directed tooth protrusions). This ensures that when the cam elements are mounted on the main camshaft body, during which the cam elements are (or can be) drawn exclusively from one direction (predetermined thread-on direction) onto the main camshaft body and during which the cam elements are substantially similar (optionally also identical) in design with regard to their hub (or their hub cross-section), the cam elements can be mounted in a simple manner. On the other hand, it is ensured that the cam elements that are fixed or are to be fixedly mounted can be slid over a multi-tooth section, which as seen in the thread-on direction is located upstream, in order (subsequently) to be able to be connected in a non-positive/positive manner to the main camshaft body in a region having an enlarged diameter located axially downstream.
In an advantageous manner, the cam elements that are to be disposed as axially non-displaceable elements on the main camshaft body can be manufactured, with regard to their hub cross-section, with considerably more clearance (increased dimensional tolerance along the lines of a so-called “clearance fit”) in comparison with the cam elements which are to be mounted in an axially displaceable manner on the main camshaft body. On the one hand, this reduces manufacturing costs and on the other hand effectively prevents these can elements from damaging the surface of a multi-tooth region when they are slid over it. The earn elements that are fixed (or are to be mounted in a non-positive/positive manner) and also the cam elements that are to be mounted in an axially displaceable manner (or are switchable) can be slid over the (multi-tooth) profile of a first sub-section of the main camshaft body. In an advantageous manner, with regard to their hub cross-section the fixed cam elements can have (optionally considerably) fewer profile teeth in comparison with the switchable cam elements, so that by reason of the increased dimensional clearance and/or the reduced number of teeth, more cost-effective production and simplified assembly (simplified sliding over the (multi-tooth) profile of a/the first axial sub-section) of the cam elements to be attached in a non-positive/positive manner are achieved.
In a particularly preferred embodiment of the method in accordance with the invention, the first and second axial sub-sections—as seen in the thread-on direction of the cam elements—are spaced apart from one another to a defined extent (end of the first sub-section to the beginning of the second sub-section), which is greater than the thickness of a cam element that is to be disposed in a rotationally fixed and axially non-displaceable manner. As a consequence, an angularly oriented alignment of the cam element that is to be drawn on only has to be performed immediately prior to pressing the cam element onto the second axial sub-section which is enlarged in terms of its diameter.
In accordance with a first embodiment of the method in accordance with the invention, the production of a built-up camshaft having at least one first axial sub-section and having at least one second axial sub-section is described, wherein as seen in a predetermined thread-on direction the second axial sub-section is located with a radial enlargement of the shaft body diameter downstream of the first axial sub-section which advantageously is formed peripherally with a multi-tooth profile extending in the axial direction. In this embodiment, the machining of the main camshaft body, with regard to the first and second axial sub-section(s) to be formed, can be performed jointly—the sequence in which the surface-machining of the two different axial sub-sections (first and second sub-section) is performed is arbitrary in this case. Then, during assembly of the cam elements on the main camshaft body, a cam element is first to be slid over at least one upstream first axial sub-section as far as against the second axial sub-section enlarged in diameter, and is to be attached in a non-positive/positive manner to the main camshaft body by means of relative displacement between the cam element and the main camshaft body. A switchable cam element is then mounted onto the first sub-section located upstream in the thread-on direction.
In accordance with a second embodiment of the method in accordance with the invention, in which as seen in the thread-on direction, starting from the free thread-on end of the main camshaft body, a second axial sub-section with a radial enlargement of the shaft body diameter is located upstream of a first axial sub-section, the sequence in which the surface-machining of the main camshaft body is performed is not arbitrary. In order not to prevent cam elements from being threaded on by reason of the shaft body diameter being enlarged at an upstream position, wherein said cam elements are to be mounted in a displaceable manner in a first axial sub-section that as seen in the thread-on direction is located downstream, the surface-machining of the at least one first axial sub-section is performed in a first machining step, the cam element that is to be disposed in a displaceable manner is then slid on with angular orientation and is positioned in the first sub-section in a rotationally fixed and axially displaceable manner, in order then to perform the surface-machining of the upstream second axial sub-section in a second surface-machining step, and the cam element which in this case is to be mounted in a rotationally fixed and axially non-displaceable manner is to be disposed on the camshaft body with angular orientation in non-positive/positive manner (by pressing). Depending upon the number and desired arrangement of fixed and switchable cam elements, the method steps of the two above-described embodiments of the method in accordance with the invention can be combined accordingly.
The main camshaft body, configured in accordance with the invention, for producing a built-up camshaft, in which once again individual cam elements are slid in a predetermined thread-on direction onto the main camshaft body, as well as the built-up camshaft itself, have in accordance with the inventive method first axial sub-sections, in which the main camshaft body surface is contoured such that a positive shaft-hub connection serves to guarantee a rotationally fixed seating of the cam element to be disposed in this sub-section in an axially displaceable manner. Furthermore, the main camshaft body comprises at least one second sub-section (in particular a sub-section that is disposed in a predetermined thread-on direction downstream of the first sub-section) with an enlarged maximum shaft body diameter, in which the main camshaft body surface is contoured such that a non-positive/positive shaft-hub connection serves to guarantee a rotationally fixed and non-displaceable seating of the cam element to be disposed in this sub-section. In a preferred manner, as seen in the thread-on direction of the cam elements, a first and a second sub-section are axially spaced apart from one another by a distance that is larger in dimension than the thickness of a cam element which is to be disposed in a second sub-section in a non-positive/positive manner on the main camshaft body.